I did just take a Race Face and XTR outer and middle ring to measure the distance between the spider arm surface that the chainring sits on, and of course they are not the same. The distance from the mounting surface to the centre of the chainring is about 1mm offset on the XTR. The middle rings are offset the same direction, so the actual space between the chairnings are both standard 3 ring spacing, but if you put just an outer RF ring on the XTR, the distance between the XTR and RF outer will be about 1mm too small. If you put an RF middle and outer on the XTR, the spacing to the granny won't be correct. If you want to use an RF granny, you'll need some spacers because XTR granny rings are thicker than anyone else's granny ring so the crank standoffs are shorter on the XTR cranks.
I'd like to put XTR rings on my RF Next cranks to get the shifting performance, but there'd be too much grinding and adjustment of the XTR rings to fit the RF spider arms.
Interestingly enough I just weighed the rings. The RF Team outer ring is 83gms and the XTR outer ring is 81gms. The RF Team middle ring is 43gms and the XTR middle ring is 43gms.
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